I placed the snippet of code to put a daily cryptogram from Cryptograms.org on my website, TheTalkBox.net. The code works, but when I complete the cryptogram and press the "Check It" button, I get the following message.

"In order to accept POST request originating from this domain, the admin must add this domain to the whitelist."

I cannot see any way to contact the administrators of Cryptograms.org, so I will post my question here in the hope that someone else has encountered this problem and can help me.